An RF Circulator is a 3-port ferromagnetic passive device designed to regulate a signal flow within a circuit. The RF circulator transmits an input signal in one direction. An example structure of a conventional RF circulator 100 is shown in FIG. 1.
The conventional RF circulator 100 includes a Y-shape conductor (e.g., metal strip) 110 placed on a ferrite substrate 120 and a permanent magnet 130 orthogonal to the Y-shape conductor 110. An RF signal input at port 101 is transmitted to port 102 and isolated from port 103. Similarly, a RF signal input at port 102 is transmitted to port 103 and isolated from port 101, and a signal input at port 103 is transmitted to port 101 and isolated from port 102. Circulators are typically designed to have minimal loss when transmitting an input signal from one port to the other. The conventional RF circulator 100 is typically packaged with a metal case (not shown in FIG. 1).
A common use of an RF circulator is to provide connectivity to an antenna. For example, an input signal is from a transmitter, which outputs at a port coupled to an antenna and isolated at a receiver port. As another example, an input signal from an antenna outputs at a port coupled to a receiver and isolated at the transmitter port.
There are a number of factors that determine the operation of an RF circulator including frequency band (or bandwidth), insertion loss, isolation, power, and package type. The bandwidth is the frequency range over which the device can operate with while providing a constant level of isolation and minimal insertion loss. An insertion loss is measured in decibels (dB) and is the loss of the input signal from one port to the next. The isolation is a measure of relative signal levels at the adjacent ports of the circulator. For example, when a signal is incident at port 101 and transmitted to port 102, the isolation is measured (in dB) between port 101 and port 103. The higher this value, the better the performance of the RF circulator. The power is the level of power in watts that the device can handle while maintaining its electrical characteristics. The package type is the form factor of the RF circulator and determines the size of the package.
Conventional RF circulators are characterized by relatively large physical size, limited bandwidth (approximately 100 MHz), and low isolation (typically 12 dB-18 dB). Although conventional RF circulators may be an alternative to cavity duplexers in base stations, due to their characteristics, they cannot be utilized, for example, in hand-held devices.
For example, the narrow bandwidth is a limiting factor for using a conventional RF circulator in cellular telephones. A telephone should operate in the entire frequency band of RF signals transmitted by the cellular telephone. In modern communication standards, the frequency band (bandwidth) of cellular telephones is about 1 GHz (for the frequency range between 1 GHz and 7 GHz, operating at a multi-band frequency). As discussed above, conventional RF circulators cannot meet this demand. In addition, the insertion loss would cause poor transmission and reception of RF signals.
It would therefore be advantageous to provide a design of a conventional RF circulator that overcomes the limitations noted above.